1. Field of the Invention
The present invention relates to a roll paper conveyance mechanism, a recording apparatus including the conveyance mechanism, and a roll paper conveyance method.
2. Description of the Related Art
The recent progress in recording technology enables numerous recording apparatuses, which are widely used in various fields, to input image data of a subject captured by an imaging apparatus (e.g., a digital camera) and record a captured image on a recording medium (e.g., a photographic printing paper). For example, if an ink ribbon and a photographic printing paper are set in advance, this kind of recording apparatus can easily perform recording processing based on acquired image data in response to a recording instruction. As an example of this kind of recording apparatus, a printer discussed in Japanese Patent Application Laid-Open No. 2008-229896 includes a cartridge capable of accommodating both an ink ribbon and a photographic printing paper.
A roll paper (i.e., a belt-like photographic printing paper wound around a roller) can be used as a photographic printing paper to be accommodated in the cartridge. The roll paper usable as a photographic printing paper is advantageous in that a great amount of photographic printing medium can be stored in a limited space of a compact cartridge. Further, a conveyance mechanism can be commonly used for various cartridges that are different in print size.
As the roll paper is constantly held in a curled state, a recording apparatus is required to include a mechanism for correcting winding curl of the roll paper. As an example, the winding curl correction mechanism discussed in Japanese Patent Application Laid-Open No. 2008-229896 includes a decurling roller. The decurling roller is made of a soft rubber and is pressed against a hard decurling driven roller, which is disposed in a confronting relationship with the decurling roller. When a roll paper moves beyond a clearance between the decurling roller and the driven roller, the roll paper travels along a curved path that is bent approximately 90 degrees. According to the above-described configuration of the winding curl correction mechanism discussed in Japanese Patent Application Laid-Open No. 2008-229896, the roll paper can be forcibly rubbed in a direction opposed to the winding direction of the roll paper in such a manner that the winding curl of the roll paper can be reduced or eliminated.
Further, a winding curl correction mechanism discussed in Japanese Patent Application Laid-Open No. 5-16476 includes a conveyance path to be pressed against an outer circumferential surface of a recording paper wound in a roll shape and having a curvature opposed to the cylindrical surface of the recording paper. According to the winding curl correction mechanism discussed in Japanese Patent Application Laid-Open No. 5-16476, the recording paper is rubbed in a direction opposed to the winding direction when the recording paper passes through the conveyance path.
The winding curl correction mechanism discussed in Japanese Patent Application Laid-Open No. 2008-229896 requires two rollers that are disposed in the conveyance path to reduce or eliminate the winding curl of a roll paper. Therefore, a roll paper conveyance mechanism for the above-described winding curl correction mechanism becomes larger in size.
In a case where a conveyance path having a curvature is provided as a winding curl correction mechanism as discussed in Japanese Patent Application Laid-Open No. 5-16476, the effect of correcting the winding curl of a roll paper is variable depending on a portion of the roll paper.
For example, when a central portion of a stretched part of the roll paper having been pulled out of a wound part of the roll paper in the longitudinal direction reaches the curved portion of the conveyance path, an upstream part of the roll paper positioned on the upstream side of the curved portion in a conveyance direction is held by a constituent member of the apparatus. In this state, if the roll paper is pulled from a downstream side in the conveyance direction, a tensile force acts on the stretched part of the roll paper having been pulled out of the wound part of the roll paper in the longitudinal direction. Therefore, the central portion of the stretched part of the roll paper tightly contacts an inner wall of the conveyance path. As a result, the central portion of the stretched part of the roll paper is rubbed by the inner wall of the conveyance path. Rubbing the roll paper in the above-described manner is useful to enhance the winding curl correction effect.
However, when a front end portion of the roll paper passes through the conveyance path, no tensile force acts on the front end portion of the roll paper. More specifically, the roll paper cannot be pulled from the downstream side when the roll paper is delivered forward. Further, when the roll paper is taken up backward, a downstream part of the roll paper cannot be firmly held. Accordingly, in both cases, the front end portion of the roll paper does not tightly contact the inner wall of the conveyance path.
As described above, if a significant amount of tensile force acts on a roll paper while the roll paper is conveyed in the conveyance path, the roll paper can be sufficiently rubbed by the inner wall of the conveyance path. In this case, the winding curl correction effect can be obtained sufficiently. On the other hand, if no tensile force acts on the roll paper while the roll paper is conveyed in the conveyance path, the roll paper does not tightly contact the inner wall of the conveyance path. The winding curl correction effect obtained in the latter case is insufficient. In particular, the winding curl correction effect at the front end portion of the roll paper is not satisfactory, as described above.
Accordingly, uniform correction effect cannot be obtained for the entire roll paper. The quality of a print product obtained by the above-described conventional apparatus may be unacceptable. The above-described problem is not limited to a case where the stretched part of the roll paper is pulled when it is conveyed. Similar problem may arise when a wound part (i.e., a rolled part) of the roll paper is pulled when it is conveyed.